Large-scale graphene production by ultrasound-assisted exfoliation of natural graphite in supercritical CO2/H2O medium

In this research, a pressure reactor coupled with an ultrasonic generator was built. The intense impact force generated from high-pressure acoustic cavitation in a supercritical CO2 (scCO(2))/H2O system and the superior penetration ability of scCO(2) were combined to enhance the exfoliation efficiency of natural graphite. The impacts of the aqueous solution content ratio, system pressure, ultrasonic power, and surfactant addition on graphite exfoliation efficiency were studied. Under optimal conditions, the graphene yield could reach more than 50% with 93% of the graphene sheets being less than three layers, and the suspension concentration could be greater than 2.5 g/L. In this approach, from raw material feeding to the discharge of products, natural graphite was directly exfoliated into high-quality graphene sheets in a few hours with a considerably high yield and concentration by using only CO2, H2O, and ethanol. This approach should be a feasible and promising method to produce high-quality graphene on a large scale and at a low cost. (C) 2016 Elsevier B.V. All rights reserved.